Planetary gear train of automatic transmission for vehicle

ABSTRACT

The present disclosure provides a planetary gear train of an automatic transmission for a vehicle. The planetary gear train may include: an input shaft receiving torque of an engine; an output shaft outputting changed torque; a first planetary gear set including first, second, and third rotation elements; a second planetary gear set including fourth, fifth, and sixth rotation elements; a third planetary gear set including seventh, eighth, and ninth rotation elements; a fourth planetary gear set including tenth, eleventh, and twelfth rotation elements.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority to and the benefit of KoreanPatent Application No. 10-2016-0028482 filed Mar. 9, 2016, which isincorporated herein by reference in its entirety.

FIELD

The present disclosure relates to an automatic transmission for avehicle. More particularly, the present disclosure relates to aplanetary gear train of an automatic transmission for a vehicle.

BACKGROUND

The statements in this section merely provide background informationrelated to the present disclosure and may not constitute prior art.

Generally, an automatic transmission achieving more speed stages hasbeen developed to enhance fuel economy and optimize drivability.

Such an automatic transmission achieving more speed stages is preferredto maximize power performance and driving efficiency according todownsizing of an engine. Particularly, we have discovered that a highefficiency multiple-speeds transmission having excellent linearity ofstep ratios can be used as an index closely related to drivability suchas acceleration before and after shift and rhythmical engine speed inorder to secure competitiveness in the automatic transmission field.

However, in the automatic transmission, as the number of speed stagesincrease, the number of internal components increase, and as a result,mountability, cost, weight, transmission efficiency, and the like maystill deteriorate.

Accordingly, development of a planetary gear train which may achievemaximum efficiency with a small number of components can increase a fuelefficiency enhancement effect through the multiple-speeds.

In this aspect, in recent years, 8-speed automatic transmissions tend tobe implemented and the research and development of a planetary geartrain capable of implementing more speed stages has also been activelyconducted.

However, since a conventional 8-speed automatic transmission has gearratio span of 6.5-7.5 (gear ratio span is an important factor forsecuring linearity of step ratios), improvement of power performance andfuel economy may not be very good.

In addition, if an 8-speed automatic transmission has gear ratio spanlarger than 9.0, it is hard to secure linearity of step ratios.Therefore, driving efficiency of an engine and drivability of a vehiclemay be deteriorated.

Further areas of applicability will become apparent from the descriptionprovided herein. It should be understood that the description andspecific examples are intended for purposes of illustration only and arenot intended to limit the scope of the present disclosure.

SUMMARY

The present disclosure has been made in an effort to provide a planetarygear train of an automatic transmission for a vehicle having advantagesof improving power delivery performance and fuel economy by achieving atleast ten forward speed stages and one reverse speed stage, and wideninggear ratio span and of securing linearity of step ratios.

One embodiment of the present disclosure provides a planetary gear trainof an automatic transmission for a vehicle having advantages ofmaintaining durability of pinion shafts by avoiding applying load toplanet carriers at stopped states when the vehicle runs at a high speedstage.

A planetary gear train of an automatic transmission for a vehicleaccording to an embodiment of the present disclosure may include: aninput shaft receiving torque of an engine; an output shaft outputtingtorque; a first planetary gear set including first, second, and thirdrotation elements; a second planetary gear set including fourth, fifth,and sixth rotation elements; a third planetary gear set includingseventh, eighth, and ninth rotation elements; a fourth planetary gearset including tenth, eleventh, and twelfth rotation elements; a firstshaft connecting the first rotation element with the fifth rotationelement and directly connected to the input shaft; a second shaftconnecting the second rotation element with the sixth rotation element;a third shaft connecting the third rotation element with the tenthrotation element; a fourth shaft connected to the fourth rotationelement; a fifth shaft connecting the seventh rotation element with thetwelfth rotation element; a sixth shaft connected to the eighth rotationelement; and a seventh shaft connected to the ninth rotation element andselectively connected to the first shaft, the second shaft, or the thirdshaft.

The fourth shaft, the fifth shaft, and the sixth shaft may beselectively connected to a transmission housing, and

The planetary gear train may further include an eighth shaft connectedto the eleventh rotation element, directly connected to the outputshaft, and selectively connected to the sixth shaft when the sixth shaftis disconnected from the transmission housing.

The first, second, and third rotation elements of the first planetarygear set may be a first sun gear, a first planet carrier, and a firstring gear, the fourth, fifth, and sixth rotation elements of the secondplanetary gear set may be a second sun gear, a second planet carrier,and a second ring gear, the seventh, eighth, and ninth rotation elementsof the third planetary gear set may be a third sun gear, a third planetcarrier, and a third ring gear, and the tenth, eleventh, and twelfthrotation elements of the fourth planetary gear set may be a fourth sungear, a fourth planet carrier, and a fourth ring gear, respectively.

The first, second, third, and fourth planetary gear sets may be disposedin a sequence of the second planetary gear set, the first planetary gearset, the fourth planetary gear set, and the third planetary gear setfrom the engine.

The planetary gear train may further include: a first clutch selectivelyconnecting the sixth shaft with the eighth shaft; a second clutchselectively connecting the first shaft with the seventh shaft; a thirdclutch selectively connecting the second shaft with the seventh shaft; afourth clutch selectively connecting the third shaft with the seventhshaft; a first brake selectively connecting the fifth shaft with thetransmission housing; a second brake selectively connecting the fourthshaft with the transmission housing; and a third brake selectivelyconnecting the sixth shaft with the transmission housing.

A planetary gear train of an automatic transmission for a vehicleaccording to another embodiment of the present disclosure may include:an input shaft receiving torque of an engine; an output shaft outputtingtorque; a first planetary gear set including first, second, and thirdrotation elements; a second planetary gear set including fourth, fifth,and sixth rotation elements; a third planetary gear set includingseventh, eighth, and ninth rotation elements; and a fourth planetarygear set including tenth, eleventh, and twelfth rotation elements,wherein the input shaft is directly connected to the first rotationelement, the output shaft is directly connected to the eleventh rotationelement, the first rotation element is directly connected to the fifthrotation element, the second rotation element is directly connected tothe sixth rotation element, the third rotation element is directlyconnected to the tenth rotation element, the fourth rotation element isdirectly connected to a transmission housing, the seventh rotationelement is directly connected to the twelfth rotation element and isselectively connected to the transmission housing, and the eighthrotation element is selectively connected to the transmission housing.

The eighth rotation element may be selectively connected to the eleventhrotation element in a state of being disconnected from the transmissionhousing, and the ninth rotation element may be selectively connected tothe first rotation element, the second rotation element, or the thirdrotation element.

The first, second, and third rotation elements of the first planetarygear set may be a first sun gear, a first planet carrier, and a firstring gear, the fourth, fifth, and sixth rotation elements of the secondplanetary gear set may be a second sun gear, a second planet carrier,and a second ring gear, the seventh, eighth, and ninth rotation elementsof the third planetary gear set may be a third sun gear, a third planetcarrier, and a third ring gear, and the tenth, eleventh, and twelfthrotation elements of the fourth planetary gear set may be a fourth sungear, a fourth planet carrier, and a fourth ring gear, respectively.

The first, second, third, and fourth planetary gear sets may be disposedin a sequence of the second planetary gear set, the first planetary gearset, the fourth planetary gear set, and the third planetary gear setfrom the engine.

The planetary gear train may further include: a first clutch selectivelyconnecting the eighth rotation element with the eleventh rotationelement; a second clutch selectively connecting the fifth rotationelement with the ninth rotation element; a third clutch selectivelyconnecting the second rotation element with the ninth rotation element;a fourth clutch selectively connecting the third rotation element withthe ninth rotation element; a first brake selectively connecting theseventh rotation element with the transmission housing; a second brakeselectively connecting the fourth rotation element with the transmissionhousing; and a third brake selectively connecting the eighth rotationelement with the transmission housing.

An embodiment of the present disclosure may achieve at least ten forwardspeed stages and one reverse speed stage by combining four planetarygear sets being simple planetary gear sets with seven control elements.

In addition, since gear ratio span greater than 10.0 is secured, drivingefficiency of the engine may be maximized.

In addition, since linearity of step ratios can be secured due tomultiple speed stages, drivability such as acceleration before and aftershift, rhythmical engine speed, and the like may be improved.

In addition, durability of pinion shafts connected to pinion gears maybe maintained due to smooth lubrication by avoiding applying load toplanet carriers at stopped states when the vehicle runs at a highforward speed stage.

DRAWINGS

In order that the disclosure may be well understood, there will now bedescribed various forms thereof, given by way of example, referencebeing made to the accompanying drawings, in which:

FIG. 1 is a schematic diagram of a planetary gear train according to anembodiment of the present disclosure.

FIG. 2 is an operation chart of control elements at each speed stage inthe planetary gear train according to an embodiment of the presentdisclosure.

The drawings described herein are for illustration purposes only and arenot intended to limit the scope of the present disclosure in any way.

DESCRIPTION OF SYMBOLS

B1, B2, B3: first, second, and third brakes

C1, C2, C3, C4: first, second, third, and fourth clutches

PG1, PG2, PG3, PG4: first, second, third, and fourth planetary gear sets

S1, S2, S3, S4: first, second, third, and fourth sun gears

PC1, PC2, PC3, PC4: first, second, third, and fourth planet carriers

R1, R2, R3, R4: first, second, third, and fourth ring gears

IS: input shaft OS: output shaft

TM1, TM2, TM3, TM4, TM5, TM6, TM7, TM8: first, second, third, fourth,fifth, sixth, seventh, and eighth shafts

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is notintended to limit the present disclosure, application, or uses. Itshould be understood that throughout the drawings, correspondingreference numerals indicate like or corresponding parts and features.

Hereinafter, an embodiment of the present disclosure will be describedin detail with reference to the accompanying drawings.

However, parts which are not related with the description are omittedfor clearly describing the embodiments of the present disclosure andlike reference numerals refer to like or similar elements throughout thespecification.

In the following description, dividing names of components into first,second, and the like is to divide the names because the names of thecomponents are the same as each other and an order thereof is notparticularly limited. As used herein, “connect” and its variantsincludes connection for transmission of force such as torque, e.g., afirst component connected to a second component for rotation therewith,or a first component connected to a second component for fixation of thecomponents, e.g. braking or resisting movement.

FIG. 1 is a schematic diagram of a planetary gear train according to anembodiment of the present disclosure.

Referring to FIG. 1, a planetary gear train according to firstembodiment of the present disclosure includes first, second, third, andfourth planetary gear sets PG1, PG2, PG3, and PG4 disposed on the sameaxis, an input shaft IS, an output shaft OS, eight shafts TM1 to TM8connected to at least one of rotation elements of the first, second,third, and fourth planetary gear sets PG1, PG2, PG3, and PG4, fourclutches C1 to C4 and three brakes B1 to B3 that are control elements,and a transmission housing H.

Torque input from the input shaft IS is changed by cooperation of thefirst, second, third, and fourth planetary gear sets PG1, PG2, PG3, andPG4, and the changed torque is output through the output shaft OS.

Herein, the planetary gear sets are disposed in a sequence of thesecond, the first, the fourth, and the third planetary gear sets PG2,PG1, PG4, and PG3 from the engine.

The input shaft IS is an input member and torque from a crankshaft ofthe engine is torque-converted through a torque converter to be inputinto the input shaft IS.

The output shaft OS is an output member, is disposed in parallel withthe input shaft IS, and transmits driving torque to a driving wheelthrough a differential apparatus.

The first planetary gear set PG1 is a single pinion planetary gear setand includes a first sun gear S1, a first planet carrier PC1 rotatablysupporting a first pinion P1 that is externally meshed with the firstsun gear S1, and a first ring gear R1 that is internally meshed with thefirst pinion P1 respectively as first, second, and third rotationelements N1, N2, and N3.

The second planetary gear set PG2 is a single pinion planetary gear setand includes a second sun gear S2, a second planet carrier PC2 rotatablysupporting a second pinion P2 that is externally meshed with the secondsun gear S2, and a second ring gear R2 that is internally meshed withthe second pinion P2 respectively as fourth, fifth, and sixth rotationelements N4, N5, and N6.

The third planetary gear set PG3 is a single pinion planetary gear setand includes a third sun gear S3, a third planet carrier PC3 rotatablysupporting a third pinion P3 that is externally meshed with the thirdsun gear S3, and a third ring gear R3 that is internally meshed with thethird pinion P3 respectively as seventh, eighth, and ninth rotationelements N7, N8, and N9.

The fourth planetary gear set PG4 is a single pinion planetary gear setand includes a fourth sun gear S4, a fourth planet carrier PC4 rotatablysupporting a fourth pinion P4 that is externally meshed with the fourthsun gear S4, and a fourth ring gear R4 that is internally meshed withthe fourth pinion P4 respectively as tenth, eleventh, and twelfthrotation elements N10, N11, and N12.

The first rotation element N1 is directly connected to the fifthrotation element N5, the second rotation element N2 is directlyconnected to the sixth rotation element N6, the third rotation elementN3 is directly connected to the tenth rotation element N10, and theseventh rotation element N7 is directly connected to the twelfthrotation element N12 by four shafts among the eight shafts TM1 to TM8.

The eight shafts TM1 to TM8 will be described in further detail.

The eight shafts TM1 to TM8 directly connect a plurality of rotationelements among the rotation elements of the planetary gear sets PG1,PG2, PG3, and PG4, and are rotation members that are directly connectedto any one rotation element (or more) of the planetary gear sets PG1,PG2, PG3, and PG4 and rotate with the any one rotation element totransmit torque, or are fixed members that directly connect any onerotation element of the planetary gear sets PG1, PG2, PG3, and PG4 tothe transmission housing H to fix the any one rotation element.

The first shaft TM1 directly connects the first rotation element N1(first sun gear S1) with the fifth rotation element N5 (second planetcarrier PC2) and is directly connected to the input shaft IS.

The second shaft TM2 directly connects the second rotation element N2(first planet carrier PC1) with the sixth rotation element N6 (secondring gear R2).

The third shaft TM3 directly connects the third rotation element N3(first ring gear R1) with the tenth rotation element N10 (fourth sungear S4).

The fourth shaft TM4 is connected to the fourth rotation element N4(second sun gear S2) and is selectively connected to the transmissionhousing H.

The fifth shaft TM5 directly connects the seventh rotation element N7(third sun gear S3) with the twelfth rotation element N12 (fourth ringgear R4) and is selectively connected to the transmission housing H.

The sixth shaft TM6 is connected to the eighth rotation element N8(third planet carrier PC3) and is selectively connected to thetransmission housing H.

The seventh shaft TM7 is connected to the ninth rotation element N9(third ring gear R3) and is selectively connected to the first, thesecond, or the third shafts TM1, TM2, or TM3.

The eighth shaft TM8 is connected to the eleventh rotation element N11(fourth planet carrier PC4), that is selectively connected to the sixthshaft TM6, and is directly connected to the output shaft OS.

In addition, four clutches C1, C2, C3, and C4 are disposed at portionsat which any two shafts among the eight shafts TM1 to TM8 including theinput shaft IS and the output shaft OS are selectively connected to eachother.

In addition, three brakes B1, B2, and B3 are disposed at portions atwhich any one shaft among the eight shafts TM1 to TM8 is selectivelyconnected to the transmission housing H.

Arrangements of the four clutches C1 to C4 and the three brakes B1 to B3are described in detail.

The first clutch C1 is disposed between the sixth shaft TM6 and theeighth shaft TM8 and selectively connects the sixth shaft TM6 with theeighth shaft TM8.

The second clutch C2 is disposed between the first shaft TM1 and theseventh shaft TM7 and selectively connects the first shaft TM1 with theseventh shaft TM7.

The third clutch C3 is disposed between the second shaft TM2 and theseventh shaft TM7 and selectively connects the second shaft TM2 with theseventh shaft TM7.

The fourth clutch C4 is disposed between the third shaft TM3 and theseventh shaft TM7 and selectively connects the third shaft TM3 with theseventh shaft TM7.

The first brake B1 is disposed between the fifth shaft TM5 and thetransmission housing H and selectively connects the fifth shaft TM5 withthe transmission housing H.

The second brake B2 is disposed between the fourth shaft TM4 and thetransmission housing H and selectively connects the fourth shaft TM4with the transmission housing H.

The third brake B3 is disposed between the sixth shaft TM6 and thetransmission housing H and selectively connects the sixth shaft TM6 withthe transmission housing H.

The control elements including the first, second, third, and fourthclutches C1, C2, C3, and C4 and the first, second, and third brakes B1,B2, and B3 may be multi-plates friction elements of wet type that areoperated by hydraulic pressure, although other types of clutches orbrakes may also be employed.

FIG. 2 is an operation chart of control elements at each speed stage inthe planetary gear train according to an embodiment of the presentdisclosure.

Referring to FIG. 2, three control elements among the first, second,third, and fourth clutches C1, C2, C3, and C4 and the first, second, andthird brakes B1, B2, and B3 that are control elements are operated ateach speed stage in the planetary gear train according to theembodiments of the present disclosure. The embodiments of the presentdisclosure can achieve one reverse speed stage and ten forward speedstages.

The first brake B1 and the second and fourth clutches C2 and C4 aresimultaneously operated at a first forward speed stage D1.

In a state that the first shaft TM1 is connected to the seventh shaftTM7 by operation of the second clutch C2 and the third shaft TM3 isconnected to the seventh shaft TM7 by operation of the fourth clutch C4,torque of the input shaft IS is input to the first shaft TM1. Inaddition, the fifth shaft TM5 is operated as the fixed element byoperation of the first brake B1. Therefore, the torque of the inputshaft IS is shifted into the first forward speed stage, and the firstforward speed stage is output to the output shaft OS connected to theeighth shaft TM8.

The first brake B1 and the second and third clutches C2 and C3 aresimultaneously operated at a second forward speed stage D2.

In a state that the first shaft TM1 is connected to the seventh shaftTM7 by operation of the second clutch C2 and the second shaft TM2 isconnected to the seventh shaft TM7 by operation of the third clutch C3,the torque of the input shaft IS is input to the first shaft TM1. Inaddition, the fifth shaft TM5 is operated as the fixed element byoperation of the first brake B1. Therefore, the torque of the inputshaft IS is shifted into the second forward speed stage, and the secondforward speed stage is output to the output shaft OS connected to theeighth shaft TM8.

The first and second brakes B1 and B2 and the second clutch C2 aresimultaneously operated at a third forward speed stage D3.

In a state that the first shaft TM1 is connected to the seventh shaftTM7 by operation of the second clutch C2, the torque of the input shaftIS is input to the first shaft TM1. In addition, the fifth shaft TM5 andthe fourth shaft TM4 are operated as the fixed elements by operation ofthe first and second brakes B1 and B2. Therefore, the torque of theinput shaft IS is shifted into the third forward speed stage, and thethird forward speed stage is output to the output shaft OS connected tothe eighth shaft TM8.

The first brake B1 and the first and second clutches C1 and C2 aresimultaneously operated at a fourth forward speed stage D4.

In a state that the sixth shaft TM6 is connected to the eighth shaft TM8by operation of the first clutch C1 and the first shaft TM1 is connectedto the seventh shaft TM7 by operation of the second clutch C2, thetorque of the input shaft IS is input to the first shaft TM1. Inaddition, the fifth shaft TM5 is operated as the fixed element byoperation of the first brake B1. Therefore, the torque of the inputshaft IS is shifted into the fourth forward speed stage, and the fourthforward speed stage is output to the output shaft OS connected to theeighth shaft TM8.

The second brake B2 and the first and second clutches C1 and C2 aresimultaneously operated at a fifth forward speed stage D5.

In a state that the sixth shaft TM6 is connected to the eighth shaft TM8by operation of the first clutch C1 and the first shaft TM1 is connectedto the seventh shaft TM7 by operation of the second clutch C2, thetorque of the input shaft IS is input to the first shaft TM1. Inaddition, the fourth shaft TM4 is operated as the fixed element byoperation of the second brake B2. Therefore, the torque of the inputshaft IS is shifted into the fifth forward speed stage, and the fifthforward speed stage is output to the output shaft OS connected to theeighth shaft TM8.

The first, second, and third clutches C1, C2, and C3 are simultaneouslyoperated at a sixth forward speed stage D6.

Since the sixth shaft TM6 is connected to the eighth shaft TM8 byoperation of the first clutch C1, the first shaft TM1 is connected tothe seventh shaft TM7 by operation of the second clutch C2, and thesecond shaft TM2 is connected to the seventh shaft TM7 by operation ofthe third clutch C3, all the planetary gear sets become lock-up states.In this state, the torque of the input shaft IS is input to the firstshaft TM1 and the sixth forward speed stage is output to the outputshaft OS connected to the eighth shaft TM8. Rotation speed that is thesame as rotation speed of the input shaft IS is output at the sixthforward speed stage.

The second brake B2 and the first and third clutches C1 and C3 aresimultaneously operated at a seventh forward speed stage D7.

In a state that the sixth shaft TM6 is connected to the eighth shaft TM8by operation of the first clutch C1 and the second shaft TM2 isconnected to the seventh shaft TM7 by operation of the third clutch C3,the torque of the input shaft IS is input to the first shaft TM1. Inaddition, the fourth shaft TM4 is operated as the fixed element byoperation of the second brake B2. Therefore, the torque of the inputshaft IS is shifted into the seventh forward speed stage, and theseventh forward speed stage is output to the output shaft OS connectedto the eighth shaft TM8.

The second brake B2 and the first and fourth clutches C1 and C4 aresimultaneously operated at an eighth forward speed stage D8.

In a state that the sixth shaft TM6 is connected to the eighth shaft TM8by operation of the first clutch C1 and the third shaft TM3 is connectedto the seventh shaft TM7 by operation of the fourth clutch C4, thetorque of the input shaft IS is input to the first shaft TM1. Inaddition, the fourth shaft TM4 is operated as the fixed element byoperation of the second brake B2. Therefore, the torque of the inputshaft IS is shifted into the eighth forward speed stage, and the eighthforward speed stage is output to the output shaft OS connected to theeighth shaft TM8.

The second brake B2 and the third and fourth clutches C3 and C4 aresimultaneously operated at a ninth forward speed stage D9.

In a state that the second shaft TM2 is connected to the seventh shaftTM7 by operation of the third clutch C3 and the third shaft TM3 isconnected to the seventh shaft TM7 by operation of the fourth clutch C4,the torque of the input shaft IS is input to the first shaft TM1. Inaddition, the fourth shaft TM4 is operated as the fixed element byoperation of the second brake B2. Therefore, the torque of the inputshaft IS is shifted into the ninth forward speed stage, and the ninthforward speed stage is output to the output shaft OS connected to theeighth shaft TM8.

The second brake B2 and the second and fourth clutches C2 and C4 aresimultaneously operated at a tenth forward speed stage D10.

In a state that the first shaft TM1 is connected to the seventh shaftTM7 by operation of the second clutch C2 and the third shaft TM3 isconnected to the seventh shaft TM7 by operation of the fourth clutch C4,the torque of the input shaft IS is input to the first shaft TM1. Inaddition, the fourth shaft TM4 is operated as the fixed element byoperation of the second brake B2. Therefore, the torque of the inputshaft IS is shifted into the tenth forward speed stage, and the tenthforward speed stage is output to the output shaft OS connected to theeighth shaft TM8.

The first and third brakes B1 and B3 and the third clutch C3 aresimultaneously operated at a reverse speed stage REV.

In a state that the second shaft TM2 is connected to the seventh shaftTM7 by operation of the third clutch C3, the torque of the input shaftIS is input to the first shaft TM1. In addition, the fifth shaft TM5 andthe sixth shaft TM6 are operated as the fixed elements by operation ofthe first and third brakes B1 and B3. Therefore, the torque of the inputshaft IS is shifted into the reverse speed stage, and the reverse speedstage is output to the output shaft OS connected to the eighth shaftTM8.

The planetary gear train according to the embodiments of the presentdisclosure may achieve at least ten forward speed stage and one reversespeed stage by combining four planetary gear sets PG1, PG2, PG3, and PG4with the four clutches C1, C2, C3, and C4 and the three brakes B1, B2,and B3.

In addition, since a gear ratio span greater than 10.0 is secured,driving efficiency of the engine may be maximized.

In addition, since linearity of step ratios can be secured due tomultiple speed stages, drivability such as acceleration before and aftershift, rhythmical engine speed, and so on may be improved.

In addition, durability of pinion shafts connected to pinion gears maybe maintained due to smooth lubrication by avoiding applying load toplanet carriers at stopped states when the vehicle runs at a highforward speed stage (higher than or equal to the seventh forward speedstage).

While this disclosure has been described in connection with what ispresently considered to be practical embodiments, it is to be understoodthat the disclosure is not limited to the disclosed embodiments, but, onthe contrary, is intended to cover various modifications and equivalentarrangements included within the spirit and scope of the appendedclaims. The description of the disclosure is merely exemplary in natureand, thus, variations that do not depart from the substance of thedisclosure are intended to be within the scope of the disclosure. Suchvariations are not to be regarded as a departure from the spirit andscope of the disclosure.

1. A planetary gear train of an automatic transmission for a vehiclecomprising: an input shaft receiving torque of an engine; an outputshaft outputting torque; a first planetary gear set including first,second, and third rotation elements; a second planetary gear setincluding fourth, fifth, and sixth rotation elements; a third planetarygear set including seventh, eighth, and ninth rotation elements; afourth planetary gear set including tenth, eleventh, and twelfthrotation elements; a first shaft connecting the first rotation elementwith the fifth rotation element and directly connected to the inputshaft; a second shaft connecting the second rotation element with thesixth rotation element; a third shaft directly connecting the thirdrotation element with the tenth rotation element; a fourth shaftconnected to the fourth rotation element; a fifth shaft connecting theseventh rotation element with the twelfth rotation element; a sixthshaft connected to the eighth rotation element; and a seventh shaftconnected to the ninth rotation element and selectively connected to thefirst shaft, the second shaft, or the third shaft.
 2. The planetary geartrain of claim 1, wherein the fourth shaft, the fifth shaft, and thesixth shaft are each selectively connectable to a transmission housing,and wherein the planetary gear train further comprises an eighth shaftconnected to the eleventh rotation element, directly connected to theoutput shaft, and selectively connected to the sixth shaft when thesixth shaft is disconnected from the transmission housing.
 3. Theplanetary gear train of claim 1, wherein the first, second, and thirdrotation elements of the first planetary gear set are a first sun gear,a first planet carrier, and a first ring gear, wherein the fourth,fifth, and sixth rotation elements of the second planetary gear set area second sun gear, a second planet carrier, and a second ring gear,wherein the seventh, eighth, and ninth rotation elements of the thirdplanetary gear set are a third sun gear, a third planet carrier, and athird ring gear, and wherein the tenth, eleventh, and twelfth rotationelements of the fourth planetary gear set are a fourth sun gear, afourth planet carrier, and a fourth ring gear, respectively.
 4. Theplanetary gear train of claim 1, wherein the first, second, third, andfourth planetary gear sets are disposed in a sequence of the secondplanetary gear set, the first planetary gear set, the fourth planetarygear set, and the third planetary gear set from the engine.
 5. Theplanetary gear train of claim 2, further comprising: a first clutchselectively connecting the sixth shaft with the eighth shaft; a secondclutch selectively connecting the first shaft with the seventh shaft; athird clutch selectively connecting the second shaft with the seventhshaft; a fourth clutch selectively connecting the third shaft with theseventh shaft; a first brake selectively connecting the fifth shaft withthe transmission housing; a second brake selectively connecting thefourth shaft with the transmission housing; and a third brakeselectively connecting the sixth shaft with the transmission housing. 6.A planetary gear train of an automatic transmission for a vehiclecomprising: an input shaft receiving torque of an engine; an outputshaft outputting torque; a first planetary gear set including first,second, and third rotation elements; a second planetary gear setincluding fourth, fifth, and sixth rotation elements; a third planetarygear set including seventh, eighth, and ninth rotation elements; and afourth planetary gear set including tenth, eleventh, and twelfthrotation elements, wherein the input shaft is directly connected to thefirst rotation element, wherein the output shaft is directly connectedto the eleventh rotation element, wherein the first rotation element isdirectly connected to the fifth rotation element, wherein the secondrotation element is directly connected to the sixth rotation element,wherein the third rotation element is directly connected to the tenthrotation element, wherein the fourth rotation element is selectivelyconnectable to a transmission housing, wherein the seventh rotationelement is directly connected to the twelfth rotation element and isselectively connected to the transmission housing, and wherein theeighth rotation element is selectively connected to the transmissionhousing.
 7. The planetary gear train of claim 6, wherein the eighthrotation element is selectively connected to the eleventh rotationelement in a state of being disconnected from the transmission housing,and wherein the ninth rotation element is selectively connected to thefirst rotation element, the second rotation element, or the thirdrotation element.
 8. The planetary gear train of claim 6, wherein thefirst, second, and third rotation elements of the first planetary gearset are a first sun gear, a first planet carrier, and a first ring gear,wherein the fourth, fifth, and sixth rotation elements of the secondplanetary gear set are a second sun gear, a second planet carrier, and asecond ring gear, wherein the seventh, eighth, and ninth rotationelements of the third planetary gear set are a third sun gear, a thirdplanet carrier, and a third ring gear, and wherein the tenth, eleventh,and twelfth rotation elements of the fourth planetary gear set are afourth sun gear, a fourth planet carrier, and a fourth ring gear,respectively.
 9. The planetary gear train of claim 6, wherein the first,second, third, and fourth planetary gear sets are disposed in a sequenceof the second planetary gear set, the first planetary gear set, thefourth planetary gear set, and the third planetary gear set from theengine.
 10. The planetary gear train of claim 7, further comprising: afirst clutch selectively connecting the eighth rotation element with theeleventh rotation element; a second clutch selectively connecting thefifth rotation element with the ninth rotation element; a third clutchselectively connecting the second rotation element with the ninthrotation element; a fourth clutch selectively connecting the thirdrotation element with the ninth rotation element; a first brakeselectively connecting the seventh rotation element with thetransmission housing; a second brake selectively connecting the fourthrotation element with the transmission housing; and a third brakeselectively connecting the eighth rotation element with the transmissionhousing.